JPH07103802B2 - Hollow airfoil - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to film cooling, and more particularly to film cooled airfoils.

It is well known that the outer surface of an airfoil is cooled by directing cooling air from the internal cavity to the outer surface through a plurality of small passages. The air flowing out of the passage is
It is preferred to remain in the boundary layer on the surface of the airfoil for as long a distance downstream of the passage as possible so as to form a protective film of cooling air between the hot main gas stream and the surface of the airfoil. The angle the passage axis makes with the airfoil surface and the relationship of the passage axis to the direction of the hot gas flow over the airfoil surface at the passage openings are important factors affecting film cooling effectiveness. Is a factor. The effectiveness E of film cooling is determined by the temperature (T
g) and the temperature (Tf) of the cooling fluid film at a distance x downstream from the outlet of the passage, the temperature difference of the main gas flow and the temperature of the cooling fluid at the passage outlet (Tc)
It is defined as the value divided by the temperature difference between and. That is, E = (Tg-Tf) / (Tg-Tc). The effectiveness of film cooling drops sharply with increasing distance x from the exit of the passage.
Maintaining high film cooling effectiveness over as large an area as possible and over as long a distance as possible is a major goal of airfoil film cooling.

In the art, the cooling air is the working fluid extracted from the compressor, which is lost from the gas flow path, resulting in a sharp drop in engine efficiency, so that the airfoil of the engine should be as small as possible. It is well known that it must be cooled with cooling air. Airfoil designers face the problem of having to cool all the airfoils of an engine using a certain minimum flow rate of cooling fluid. The amount of the cooling fluid flowing from the internal cavity into the gas passage through the individual cooling fluid passages is controlled by the minimum sectional area (measuring area) of the cooling fluid passage. The metering area is typically located where the passage intersects the internal cavity. Assuming that the internal and external pressures are constant or at least beyond the control of the designer, the entire metering area of all cooling fluid passages and orifices from the interior of the airfoil will cover all of the cooling fluid from the airfoil. Control the flow rate. Designers must ensure that all areas of the airfoil are maintained below the critical design temperature limit, which is determined by points that must be considered in terms of airfoil material capabilities, maximum stress, and life requirements. The size of, the distance between passages, the shape and direction of the passages must be specified.

Ideally, 100% of the airfoil surface should be covered with a film of cooling air, but the air exiting the aisle outlet is generally no wider or almost wider than the dimensions of the aisle outlet perpendicular to the gas flow. Not forming a band of cooling film. Due to restrictions on the number, size, and spacing of cooling fluid passages,
Gaps are formed between the protective films, and regions where the film cooling efficiency is low are generated, which causes local hot spots. Airfoil hotspots are one factor that limits the operating temperature of an engine.

In U.S. Pat.No. 3,527,543, cooling fluid from a given passage stays better in the boundary layer.
A divergent tapered passage with a circular cross section is used. In addition, in the plane where the passage extends in the longitudinal direction or to some extent in the gas flow direction, the cooling fluid diffuses in the longitudinal direction when the cooling fluid flows out of the passage and moves in the downstream direction. It is preferably oriented so that Despite this construction, an oval passage opening (US Pat. No. 3,527,
No. 543), the longitudinal width of the cooling fluid film expands in the longitudinal direction only to the length of the minor axis of at most one passage outlet after the cooling fluid is discharged to the surface of the airfoil. I understand. Due to this fact and the fact that the longitudinal spacing between the passages is 3 to 6 times the diameter, the surface of the airfoil has its rows in the region between the longitudinally spaced passages and in its downstream region. There is a portion that does not receive the cooling fluid from the passage of. The conical inclined passages described in U.S. Pat. No. 3,527,543 only provide coverage of at most 70% (percentage of the center-to-center distance of adjacent passage openings covered by cooling fluid). .

The velocity of the air exiting the cooling fluid passage is dependent on the ratio of the air pressure at the passage inlet to the gas flow pressure at the passage outlet. Generally, the higher this pressure ratio, the higher the exit velocity. If the outlet velocity is too high, cooling air will flow through the gas stream and be carried away by the gas stream without effective film cooling. Conversely, if the pressure ratio is too small,
The gas flow penetrates into the cooling fluid passages, resulting in localized incomplete cooling of the airfoil. Incomplete cooling of the airfoil generally has detrimental consequences, which generally provides a margin of safety. This extra pressure for safety margins forces the design to have a high pressure ratio. A high pressure ratio margin is one preferred feature of film cooling structures. U.S. Pat.
Diffusing the flow of cooling air by tapering the passages as described in US Pat. No. 543 is beneficial in providing such a margin, but as described in this U.S. Pat. Smaller (up to 12 ° angles), to reduce the exit velocity to what is believed to be the most favorable for reducing the susceptibility of the membrane cooling structure to the pressure ratio, the passage is lengthened and therefore the airfoil The wall becomes thicker. The same limitation exists in the trapezoidal diffusion passages described in US Pat. No. 4,197,443. The maximum diffusion angle in the two mutually perpendicular planes described in this U.S. patent is that the cooling fluid does not separate from the tapered walls and that the cooling fluid is in a gas flow that is hotter than the passages. They are set at 7 ° and 14 °, respectively, to ensure that the passage is completely filled as it flows out. Due to this limitation on the diffusion angle, the walls of the airfoil are thickened, and the passages in the airfoil are only widened by sloping the passages in the span direction, and the longitudinal spacing between passages is also increased. Can be made smaller. While a large diffusion angle is preferred, this cannot be achieved by the prior art.

2 and 3 of JP-A-55-114806 (reproduced as FIGS. 9 and 10 in the present application),
A hollow airfoil is described having linear cylindrical passages arranged in longitudinally extending rows, the passages leading to longitudinally extending grooves formed in the outer surface of the airfoil. In this application, the cooling fluid flows from adjacent passages mix with each other and a uniform thickness of cooling is achieved over the entire length of the groove by the time the cooling fluid exits the groove and reaches the surface of the airfoil. Although forming a film of fluid is described, tests conducted by the inventors have shown that the cooling fluid from the cylindrical passage has a substantially constant width (substantially equal to the diameter of the passage). It was found that the belt moved to the downstream side. Diffusion caused by the mixing of adjacent bands of cooling fluid occurs far downstream, so the effectiveness of film cooling at that point is less than that required for many airfoil constructions. Is also much lower.

U.S. Pat. No. 3,515,499 describes an airfoil consisting of a stack of etched wafers. The finished airfoil has a plurality of longitudinally spaced passages extending from the inner cavity to a common longitudinally extending groove that releases cooling air to form a film of cooling air on its outer surface. Includes several areas that have.
In FIG. 1 of this U.S. patent, each passage tapers from its inlet to the area of the smallest cross-sectional area where it intersects the groove. Also, in another embodiment of FIG. 9 of this U.S. Patent, the passageway has a small constant size and leads to a fairly wide groove. Both of these structures are disclosed in
It has the same drawbacks as described for 55-114806, in that the cooling fluid does not evenly fill the groove before it enters the main gas stream, and the film at the downstream side of the groove is The coverage is much lower than 100%.

Other publications relating to film cooling the outer surface of an airfoil include U.S. Patent Nos. 2,149,510 and 2,220,420.
No. 2,489,683, published on March 16, 1956, "Flight and Aircraft Engineer (Flig
ht and Aircraft Engineer) '' No.2460, Vol.69 (292 ~
295), which disclose the use of longitudinally extending grooves to cool the pressure and suction sides of the leading edge or airfoil. The grooves described in these publications extend completely through the wall of the airfoil so that they are in direct communication with the internal cavity. These grooves are not preferable from the viewpoint of structural strength, and these grooves inevitably have a very large flow rate.

U.S. Pat. No. 4,303,374 describes a structure for cooling the undercut exposed surface of the trailing edge of an airfoil. The structure includes a plurality of longitudinally spaced divergent passages in the trailing edge. Adjacent passages are proximate to each other at their outlet ends, forming a continuous film of cooling air on the undercut surface.

Published in 1971 by the Academic Press in New York, USA, "Advances in Heat Transfer"
Heat Transfer) "(edited by TFIrvine, Jr. and JP Hartnett), Volume 7, pages 321-379, gives an overview of film cooling technology. An article entitled "Film Cooling," written by Richard J. Goldstein, is included. This article describes various shaped elongated grooves that extend completely through the wall to be cooled, and channels of circular cross section that extend through the wall.

DISCLOSURE OF THE INVENTION One object of the present invention is to provide a hollow airfoil with improved film cooling of its outer surface.

Another object of the invention is to provide a film cooling structure for the walls of hollow airfoils which reduces the risk of blockage of individual cooling body fluid passages.

Yet another object of the present invention is to provide a film cooling structure for the walls of a hollow airfoil that forms a continuous film of cooling fluid that extends longitudinally across the outer surface of the airfoil. is there.

According to the invention, the wall of the hollow airfoil has a longitudinally extending groove provided in its outer surface and a longitudinal row of cooling fluid passages extending through the wall, Each passage has a metering portion provided at its inner end and a diffusing portion provided at its outer end, and the wall surface of the diffusing portion is divergent in the longitudinal direction toward the outer surface of the airfoil. , The divergent wall surfaces of adjacent passages meet each other substantially at the bottom of the groove inside the outer surface of the airfoil, whereby each passage communicates with the groove and fills the groove with cooling fluid. As such, the cooling fluid exits the groove as a continuous film extending longitudinally on the outer surface of the airfoil downstream of the groove.

The surfaces of the passages and grooves are beveled so that the cooling fluid can be guided in a direction having a velocity component in the downstream direction and at a small angle to the outer surface, whereby the cooling fluid is bounded when it exits the groove. In the layer, it is attached to the outer surface of the airfoil as a thin film. By using cooling fluid passages that are divergent when viewed in longitudinal section, and also in such a way that there is very little or no spacing between their outlets where adjacent passages intersect the bottom of the groove. By placing the passages sufficiently close to each other in one row of the cooling fluid, the cooling fluid diffuses further in the groove,
The groove is completely filled over its entire extent in its longitudinal direction before it enters the hot gas stream. With such a configuration, a small amount of cooling fluid can be diffused as a continuous film over substantially the entire length of the airfoil in the longitudinal direction.

Yet another advantage of the present invention is that debris within the gas flow path is less likely to block the flow of cooling fluid through the individual cooling fluid passages. If the cooling fluid passages were opened at the outer surface of the airfoil as small outlets independent of each other, debris could stagnate at the outlet and block the passage. According to the invention, debris is likely to remain stagnant between the side walls of the groove, so that the outlets of the individual passages are not blocked. That is, the cooling fluid can flow around the debris through the passage.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION As an exemplary embodiment of the present invention, a turbine blade generally designated by reference numeral 10 will be described. 1 and 2, the blade 10 is a hollow airfoil.
12 includes an airfoil 12 extending in a spanwise or longitudinal direction from an integral root 14 thereof. Platform at the base of the airfoil 12
16 are provided. The airfoil 12 includes a wall 18 having an outer surface 20 and an inner surface 22. The inner surface 22 defines a longitudinally extending internal cavity that is adjacent to each other by longitudinally extending ribs 30 and 32 and is longitudinally extending to a plurality of compartments 24, 26, 28.
Is divided into A passage 34 provided in the route 14 is in communication with the compartment 24, and a passage 36 provided in the route 14 is in communication with the compartments 26 and 28. When the blades 10 are operated in their intended environment, such as the turbine section of a gas turbine engine, pressurized cooling fluid from a suitable source, such as compressor bleed air, is passed through passages 34 and 36. Into the compartments 24, 26, 28, which pressurizes them.

In the accompanying drawings, arrow 40 indicates the direction of flow (ie, streamline) of the hot gas flowing over the surface of the airfoil.
For purposes of describing the invention, the flow direction of hot gas flowing over the pressure side or suction side of the airfoil is referred to as the downstream direction. Thus, at any point on the airfoil suction or pressure side, the downstream direction is tangential to the airfoil surface and close to the airfoil tip or platform 16 where irregular flow is generated. With the exception of the base of the foil, the downstream direction is substantially perpendicular to the span direction of the airfoil.

In accordance with the present invention, the pressurized cooling fluid in compartments 24, 26, 28 is supplied with cooling fluid via a passageway through wall 18, such as passageway 41, or by a passageway 44 described in detail below. Outflow from the airfoil via 42 cools the outer surface 20 of the airfoil wall 18. In one typical turbine blade airfoil, there may be multiple rows of passages, such as passage 41, which are provided on both the pressure and suction sides of the airfoil, and Located around the leading edge of the airfoil. For clarity and brevity only a few rows of passages are shown in the accompanying figures. Thus, the illustrated airfoil is for the purpose of illustrating the invention and is not intended to limit the scope of the invention.

1-6, in accordance with the present invention, the longitudinally extending groove 42 in the outer surface 20 of the airfoil includes wall surfaces 48 and 50 spaced from each other and facing each other. The walls of the are connected to each other by the bottom surface 52 of the groove. Wall
48 and 50 are substantially parallel to the longitudinal direction. Wall 48
And 50 in view of their position with respect to the downstream direction 40, will be referred to hereinafter as the front face 48 and the rear face 50, respectively. That is, it is considered that the wall surface 50 is located on the downstream side of the wall surface 48, and thus is located behind it. The front surface 48 intersects the outer surface 20 and forms the upstream edge 54 of the groove 42, and the rear surface 50 is the outer surface 20.
Intersects with to form a downstream edge 56 of the groove 42. These surfaces 48 and 50 preferably intersect the outer surface 20 at a relatively small angle of about 45 ° or less.

The passages 44 are substantially longitudinally aligned along the length of the groove 42. Each passage 44 has a measuring portion 58 provided at its inner end.
And a diffusion portion 60 provided at the outer end portion thereof in a serial flow relationship. In this embodiment, the metering section 58 is straight and its cross section perpendicular to the central axis 62 is a substantially rectangular constant section, the central axis 62 being the geometrical shape of the metering area. It goes through the center. The metering portion 58 intersects the inner surface 22 and defines an entrance 64 to the passage. Weighing section exit
66 coincides with the entrance to the diffusion section 60.

As best shown in FIG. 4, the diffusing section 60 includes a pair of end walls 68 and 70 spaced from each other and facing each other, the surfaces of which are located from the outlet 66 of the metering section. The bottom surface 52 of the intersecting groove has a divergent shape when viewed in a longitudinal section.

In FIG. 3, each passage 44 includes a pair of side wall surfaces 72 and 74 spaced from each other and opposed to each other, these surfaces being connected along their length with end wall surfaces 68 and 70. And is connected to the rear surface 50 and the front surface 48 of the groove. Side wall surfaces 72 and 74 are substantially parallel to the longitudinal direction. In this embodiment, the sidewall surface 74 extends coplanar with the groove front surface 48 and is parallel to the central axis 62. Central axis 62
The angle P between the outer surface 20 and the outer surface 20 is preferably less than about 45 °, in particular 25-40 °. The side wall surface 72 extends in the same plane as the rear surface 50 of the groove, and has a divergent shape in the downstream direction at an angle indicated by the symbol R from the central axis 62 and the side wall surface 74. preferable. The divergence angle R is preferably in the range of about 5 ° to 10 °. Since the rear surface 50 has a divergent shape in a direction away from the central axis 62, an angle S formed by the rear surface 50 and the outer surface 20 of the airfoil is reduced downstream of the groove. This allows the cooling fluid to easily collect in the boundary layer downstream of the groove. Angle R
May be 0 ° and still fall within the scope of the invention.

In FIG. 4, the end wall surfaces 68 and 70 are diffused in the direction away from the central axis line 62 at the angle indicated by the symbol T, respectively. Thus, the end wall surfaces 68 and 70 are divergent in the direction away from each other at an angle of 2T. The spacing between adjacent passages 44, ie the pitch p and the angle T, is such that
The end walls 68 and 70 adjacent to each other are substantially the bottom surface 52 of the groove.
Will be selected to meet each other. This improves the complete filling of the groove as the cooling fluid exits the passage. In order to reduce the number of passages, it is desirable that the angle T is at least about 10 °, but if the angle T is too large, the cooling fluid flowing out of the metering section will not adhere to the end wall surfaces 68 and 70. . In that case, the cooling fluid not only fills the diffusing portion, but also does not diffuse sufficiently in the groove, and a continuous film of the cooling fluid is not formed along the length of the groove.

FIG. 7 is an illustration similar to FIG. 4 showing another embodiment of the present invention. In FIG. 7, the end wall surfaces 68 'and 70' are effective diffusion angles T '(the end wall surfaces 68' and 70 'are respectively one flat surface extending from the start point of the end wall surface to the end point of the end wall surface). In order to form the angle (formed in some cases), it is diffused from the central axis 62 'in two steps. This effective divergence angle T'should be at least 10 °.

The cooling fluid passages and grooves of the present invention may be formed by any suitable means. One preferred method is the well-known electrical discharge machining (EDM) method which is carried out using electrodes having the shape of the passages and grooves to be formed. A plurality of passages may be formed simultaneously using a comb electrode as shown in FIG. 8 which is an electrode having a plurality of adjacent teeth 80 each having the shape of a passage 44. The teeth are connected to each other by a common base portion 82. The electrode is moved into the work piece over a distance greater than the length of the tooth 80, such as up to the reference line 84 in FIG. Thus, the portion between the reference line 84 of the base portion 82 and the root of the tooth 80 forms the groove 42 on the surface of the work piece. Base part
Reference numeral 82 is appropriately formed in a tapered shape so as to give a proper groove shape in the above portion.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art.

[Brief description of drawings]

FIG. 1 is a front view showing a hollow turbine blade incorporating the present invention with a part thereof cut away. 2 is a sectional view taken along line 2-2 of FIG. FIG. 3 is an enlarged partial sectional view of a portion indicated by line 3-3 in FIG. FIG. 4 is a sectional view taken along the line 4-4 in FIG. FIG. 5 is a view taken along the line 5-5 in FIG. FIG. 6 is an enlarged partial view of the portion indicated by line 6-6 in FIG. FIG. 7 is a sectional view similar to FIG. 4 showing another embodiment of the present invention. FIG. 8 is a perspective view showing an electrode that may be used to form the cooling fluid passages and grooves of the present invention. FIG. 9 and FIG. 10 are respectively the second of JP-A-55-114806.
It is a solution figure corresponding to Drawing and Drawing 3. 10… Turbine blades, 12… Airfoils, 14… Roots, 16… Platforms, 18… Walls, 20… Exterior, 22… Interior, 2
4, 26, 28… Compartments, 30, 32… Ribs, 34, 36, 4
1 ... Passage, 42 ... Groove, 44 ... Passage, 48, 50 ... Wall, 52 ... Bottom, 54 ...
Upstream edge, 56 ... Downstream edge, 58 ... Weighing section, 60 ... Diffusion section, 62 ... Central axis, 64 ... Inlet, 66 ... Outlet, 68, 70 ... End wall surface, 7
2, 74 ... Side wall surface, 80 ... Tooth, 82 ... Base part, 84 ... Reference line

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-60-32903 (JP, A) JP-A-58-172407 (JP, A) JP-A-62-168904 (JP, A) JP-A-62- 168903 (JP, A)

Claims (1)

[Claims] 1. A hollow airfoil for a turbomachine, the airfoil being configured to be disposed in a stream of hot gas flowing in a downstream direction, the airfoil defining an outer surface thereof. An outer wall, the outer wall having an inner surface defining a portion of a longitudinally extending compartment for receiving a cooling fluid within the airfoil, the outer wall having a longitudinal direction formed in the outer surface. Including a groove extending to the front wall surface, the groove having a front wall surface, a rear wall surface facing the front wall surface, and a bottom surface, the bottom surface extending between the front wall surface and the rear wall surface. The front wall surface and the rear wall surface each intersect with the outer surface of the airfoil at an acute angle and flow upstream toward the outer surface of the airfoil so as to allow the cooling fluid to flow downstream. Side edge and bottom A side edge is defined, and the outer wall is formed with a plurality of cooling fluid passages extending therethrough and spaced from each other along the longitudinal direction of the airfoil. Each of which is in fluid communication with the compartment and receives a cooling fluid from the compartment to measure a flow rate of the cooling fluid flowing through the cooling fluid passage; and an outer portion connected in series to the inner portion. And the outer portion includes end wall surfaces that are divergent toward the bottom surface of the groove and that are divergent toward the bottom surface and are spaced apart from each other and that face each other. The end wall surfaces adjacent to each other of the passage meet each other substantially at the bottom surface of the groove,
The outer portion of each of the cooling fluid passages includes side wall surfaces that connect the end wall surfaces and are spaced from each other and face each other, and one of the side wall surfaces is connected to the front wall surface of the groove. A hollow airfoil in which the other of the side wall surfaces is connected to the rear wall surface of the groove.